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Is the soil too dry to apply anhydrous ammonia?

Dry soils are a challenge to in-soil banded nitrogen application, especially anhydrous ammonia. When anhydrous ammonia is injected into soil the ammonia (NH3) is dissolved in water and reacts to convert to ammonium (NH4+), which is positively charged and held by the cation exchange on the soil particles.

Soil moisture is needed to allow the ammonia to convert and be retained in the soil, however even in dry soils there is usually enough moisture present for this to occur. The major problem with dry soils is the clods or lumps that form can prevent a good seal, allowing the ammonia to be lost through large voids between clods before dissolution in moisture occurs. Indeed, nitrogen losses on low moisture soils are caused more by poor physical soil structure (soil tilth) than by a lack of moisture to chemically react with ammonia.

Clay soils that are very dry will be cloddy or lumpy and may permit too much gaseous ammonia to escape. The zone of ammonia dissipation from the injection point is larger in dry soil, so although the soil may be difficult to work, deeper injection may actually be required. Lighter textured soils will have better tilth than dry clay soils and will be more likely to produce a good seal to retain the ammonia.

Slot closure may be better on previously worked than on uncultivated soils if the soil flows and seals better. Such is not the case if soils were cloddy. Some cereal crops were harvested almost 2 months ago and the moisture that has been received may be sufficient to provide good tilth. Soil moisture and texture varies across the province, as does farm equipment. The only way to assess your soil conditions is a test run with your applicator. An application pass without N will indicate whether soils are too cloddy and injection slot closure is inadequate. If after making a round with N, you can still smell ammonia from the previous application, make adjustments in depth or closure modifications. Or wait for rainfall to improve soil structure.

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Reference material

Diseases: New clubroot cases have been confirmed in the Rural Municipalities of Lorne and Dufferin. Insects: Scouting for bertha armyworm continues with some reports of insecticide applications. Spider mites being noticed in some soybean fields. Grasshopper populations are variable. For full report see Insect & Disease Report – August 1, 2018

Crops are advancing rapidly with the warm and dry conditions. Rain is needed in most areas to sustain crops and replenish soil moisture. Harvested has started in winter cereals, barley, and peas. Swathing or pre-harvest applications have started in early seeded spring cereals and canola. Fist cut hay is nearing completion; yields are below normal. […]

Diseases: The second case of clubroot in canola this year has been reported. Disease surveys in soybean and wheat are ongoing and disease levels are low overall. Insects: Overall insect concerns in field crops are relatively low. There are still some areas where grasshopper levels are being watched. Spider mite levels are being monitored in some soybean fields in […]

Disease – Goss’s wilt was observed near St. Claude. Insects – Grasshopper populations are being monitored in and around the edges of some fields. Armyworms have been noticed in some cereal fields in the Central and Eastern regions. No soybean aphids have been reported yet. For more details and information see http://www.gov.mb.ca/agriculture/crops/seasonal-reports/manitoba-insect-and-disease-update-2018-07-11.html

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Favourable weather and field conditions have allowed seeding operations to begin, with a provincial estimate of <5% of the 2017 crop seeded. For the full crop report, see on-line at http://www.gov.mb.ca/agriculture/crops/seasonal-reports/crop-report-archive/crop-report-2017-05-01.html

The Guide to Crop Protection provides information on the use of herbicides, fungicides and insecticides for control of weeds, plant diseases and insects. This publication is only a guide. Always refer to the product label for application details and precautions. It is available: online at https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp. Individual sections on Weed Control, Plant Disease Control and Insect […]

Did you know you can view the 2017 edition of Seed Manitoba, as well as past editions, on www.seedmb.ca? Well, you can! Flip-view digital editions of the current guide (2017), as well as the six most recent editions, are available at http://www.seedmb.ca/digital-edition/. Also, full PDF versions are available at http://www.seedmb.ca/digital-edition/pdf-editions-and-separate-section-pdfs/ where you can download the entire […]

http://www.gov.mb.ca/agriculture/crops/plant-diseases/clubroot-distribution-in-manitoba.html Map shows positive clubroot findings by Rural Municipality, discovered through laboratory testing for presence of clubroot spores in soil and/or positive confirmation of clubroot symptomatic plants. Testing was done from 2009-2014 and is still considered limited. Positive findings have been at low spore concentrations and sporadic throughout the province. As more fields are sampled, the map will be updated. As less than […]